The invention generally relates to image detection and specifically automated image detection.
Corneal haze describes a cloudy or opaque appearance of the cornea, as shown in FIG. 1. It is most often caused by inflammatory cells and other debris activated during trauma, infection, or eye procedures and surgeries such as crosslinking for keratoconus eyes and refractive surgeries (i.e., LASIK). The cornea is normally clear and corneal haze can occur in any part of the cornea, thus it can greatly impair vision. A demarcation line indicates the transition zone between cross-linked anterior corneal stroma and untreated posterior corneal stroma; it is biomicroscopically detectable as early as 2 weeks after treatment. The presence and depth of the demarcation line is an easy and useful tool for clinicians to assess the corneal cross-linking effect and determining the efficacy of the procedure.
The backscattered light from a normal (clear) cornea is typically low, but in corneal dystrophies or after injury, corneal haze can be associated with pathology that often indicates the corneal structures responsible for poor vision. Thus, changes in haze and demarcation line can be used to track progression of disease or response to treatment such as crosslinking or refractive surgery. More importantly, observation of haze has been very valuable to ophthalmologists because the same processes that produce haze are often responsible for forward scatter that degrades vision. Similarly, the presence and depth of the demarcation line reflects the success of the surgery and/or treatment.
To date, clinical instruments for measuring haze have included custom modified slit-lamps, clinical confocal microscopes, and Scheimpflug cameras. The spatial resolution needed to identify the source of the backscattered light varies among instruments. Some slit-illumination instruments can only resolve approximately two thirds of the full corneal thickness, while the depth of field with confocal microscopes has been reported from 4 to 26 μm.
Therefore, quantification of corneal haze by means of an objective method that can adequately assess the overall amount of opacification, coupled with analysis of its regional variations within the cornea relative to the ablation zone, would lead to better understanding of the phenomenon. Furthermore, standardizing image brightness in optical coherence tomography (OCT) images and developing the technology for automatically detecting and classifying corneal haze will offer objective view of the cornea and may improve clinical decision-making after corneal surgeries such as crosslinking and LASIK.
Furthermore, the demarcation line can be manually observed by a human operator using the OCT scanner interface; however, the process is tedious and time consuming; the experienced operator will have to observe many OCT sections of the cornea and determine the demarcation line among other reactive and non-specific hazy lines that can mimic the actual demarcation line. Subsequently, the operator would need to use a digital caliper to evaluate the line depth. Most importantly, the whole evaluation is in part subjective and operator-dependent, with intra-observer repeatability and inter-observer reproducibility not yet investigated. Thus, automated detection and measurement of the demarcation line depth can become “the standard of care” in cross-linking surgery in assessing treatment success. By the same token, software analysis of stromal haze could potentially become instrumental in objectively assessing cross-linking side effects.
Optical Coherence Tomography is a non-invasive, in-vivo imaging technique based on the back-scatter or reflectivity of light in a medium (see, e.g., Huang et al. 1991). In ophthalmic examinations, the beam of light produced by the OCT device scans the eye through the pupil and the image formation process records the back-scattering profile of the light at each location. The amount of scatter is indicative of the reflectivity of the tissue encountered, and a grayscale cross-sectional image is formed as the light beam sweeps across the field of view (FOV). OCT imaging has dramatically advanced ophthalmic diagnostic capabilities and led also to better understanding of ocular anatomy. It is now an established basis of routine ophthalmic practice. Several implementations of OCT have been developed including time domain (TD-OCT) and frequency domain (FD-OCT) which covers both spectral domain (SD-OCT) and swept-source (SS-OCT). The present invention attempts to solve these problems as well as others.